<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>结构伪类选择器-empty</title>
    <style>
       div{
           width: 100px;
           height: 100px;
       }

       div:empty{
           background: yellow;
       }
       /* 空格也不行 */
    </style>
</head>
<body>
    <div>
       1111
    </div>

    <div>
        
     </div>

    <div></div>
</body>
</html>